1. Field of the Invention
The present invention relates to a pattern defects inspection system which utilizes graphic data processing to detect the presence/absence of pattern defects in a sample (e.g., a reticle) on which a pattern, e.g., a photomask used in the process of manufacturing a semiconductor integrated circuit (LSI) or an LCD is formed.
2. Description of the Related Art
In general, in the process of manufacturing an LSI or an LCD, one of the main causes for a decrease in yield is the presence of pattern defects in a photomask used in the process. For this reason, some inspection systems for inspecting such pattern defects have been enthusiastically developed and have already been put into practical use.
FIG. 11 shows the arrangement of an inspection apparatus of the system exemplifying the above-mentioned conventional pattern defects inspection system. More specifically, in this system, the pattern formed on a photomask 1 is enlarged by using an optical system such as a microscope. The enlarged pattern is divided into continuous narrow strips, each having a width W of, e.g., about 500 .mu.m, as shown in FIGS. 12A and 12B. Detection of pattern defects is performed by continuously scanning these divided portions. (Note that in practice, a table is continuously moved at intervals of a predetermined length P.)
A photomask 1 is placed on an XY.theta. table 2. A predetermined pattern (e.g., an F-shaped pattern) formed on the photomask 1 is illuminated by a light source 3. Light transmitted through the photomask 1 is incident on a photodiode array 5 through a magnifying optical system (e.g., a lens) 4. As a result, an optical image of the pattern is formed on the photodiode array 5. The pattern image formed on the photodiode array 5 is photoelectrically converted by the photodiode array 5. The resultant data is A/D-converted by a sensor circuit 6. Measurement pattern data output from the sensor circuit 6 is supplied to a data comparator 8 together with data output from a positioning circuit 7 and indicating the position of the photomask 1 on the XY8 table 2.
Meanwhile, the pattern design data used to form the pattern on the photomask 1 is read out from a magnetic disk unit 9 and is loaded into a bit pattern generator 11 through a CPU 10. The bit pattern generator 11 converts pattern design data, stored in a magnetic disk (DK) or the like, into binary bit data, and supplies the bit data to the data comparator 8. The data comparator 8 performs predetermined filtering processing with respect to the supplied bit data associated with a graphic pattern so as to convert the data into multivalued (base-n number: plurality of digitized value) data. The reason why this processing is required is that since the measurement pattern data obtained by the sensor circuit 6 has undergone filtering processing based on the resolution characteristics of the magnifying optical system 4, the aperture effect of the photodiode array 5, and the like, the pattern design data needs to be filtered to conform to the data format of the measurement pattern data. The data comparator 8 compares the measurement pattern data with the filtered design data in accordance with a predetermined algorithm, and determines the presence of defects in the pattern if the two data do not coincide with each other.
In order to satisfy the demand for LSIs having higher integration densities, an increase in resolution of an optical transfer unit is demanded. In recent apparatuses, in order to meet such a demand, it is proposed that a phase shift pattern utilizing interference of light be formed on a photomask. More specifically, a pattern formed on the photomask 1 shown in FIG. 13 is roughly divided into a peripheral pattern 21 and a circuit pattern 22. The circuit pattern 22 is further divided into a logic/controller portion 23 and a memory portion 24. It is required that a fine pattern be formed especially on the memory portion 24. It is, therefore, required to form a phase shift pattern on the memory portion 24.
An ordinary photomask is generally obtained by forming a layer having a light-shielding function (the property of shielding light), e.g., a chromium layer on the surface of a glass substrate to have a predetermined pattern (to be referred to as a chromium pattern or a light-shielding pattern hereinafter). A phase shift pattern is generally formed from a transparent material such as SiO.sub.2.
Various phase shift structures are formed by different schemes, e.g., the Levenson scheme shown in FIG. 14A, the auxiliary pattern scheme shown in FIG. 14B, the edge emphasis scheme shown in FIG. 14C, the chromium-less scheme shown in FIG. 14D, and the halftone scheme shown in FIG. 14E. Note that a glass substrate 25, a chromium pattern 26, and a phase shift pattern 27 are common portions throughout these drawings.
It is currently required for a pattern defects inspection system to have a function of inspecting pattern defects including phase shift pattern defects with high accuracy. However, the conventional pattern defects inspection system shown in FIG. 11 cannot simultaneously inspect defects in both a chromium pattern and a phase shift pattern which are formed on a sample, e.g., a photomask, together.
As described above, the conventional apparatus of pattern defects inspection system inspects pattern defects by comparing pattern design data used to form a pattern with measurement data obtained by actual measurement. In such an apparatus, however, when pattern defects are to be inspected in a sample such as a photomask having both a chromium pattern and a phase shift pattern, defects in the two patterns cannot be simultaneously inspected. More specifically, since, in an operation of the conventional apparatus, defects in a chromium pattern and those in a phase shift pattern are inspected separately (e.g., at least twice), the time required for such an operation is twice that required for one inspecting operation.